THE PROCEDURAL GENERATION OF INTERESTING SOKOBAN LEVELS Joshua Taylor, B.S., M.S. Dissertation Prepared for the Degree of DOCTOR OF PHILOSOPHY UNIVERSITY OF NORTH TEXAS May 2015 APPROVED: Ian Parberry, Major Professor Robert Akl, Committee Member Armin R. Mikler, Committee Member Robert Renka, Committee Member Barrett R. Bryant, Chair of the Department of Computer Science and Engineering Costas Tsatsoulis, Dean of the College of Engineering and Interim Dean of the Toulouse Graduate School Taylor, Joshua. The Procedural Generation of Interesting Sokoban Levels. Doctor of Philosophy (Computer Science and Engineering), May 2015, 69 pp., 32 tables, 11 figures, references, 46 titles. As video games continue to become larger, more complex, and more costly to produce, research into methods to make game creation easier and faster becomes more valuable. One such research topic is procedural generation, which allows the computer to assist in the creation of content. This dissertation presents a new algorithm for the generation of Sokoban levels. Sokoban is a grid-based transport puzzle which is computational interesting due to being PSPACE-complete. Beyond just generating levels, the question of whether or not the levels created by this algorithm are interesting to human players is explored. A study was carried out comparing player attention while playing hand made levels versus their attention during procedurally generated levels. An auditory Stroop test was used to measure attention without disrupting play. Copyright 2015 by Joshua Taylor ii ACKNOWLEDGEMENTS I would like to thank Marcus Hof, David Holland, Evgeny Grigoriev, David W. Skinner, and Rick Sladkey for giving me permission to use their Sokoban levels in my study. I would like to thank Dr. Thomas Parsons, Paeng Angnakoon, and Marvin Powell for their help in designing and analyzing my study. Finally, I would like to thank my wife for putting up with my extended tenure as a student. iii TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................... iii LIST OF TABLES ......................................................................................................... vi LIST OF FIGURES ..................................................................................................... viii CHAPTER 1 INTRODUCTION ..................................................................................... 1 1.1. Procedural Generation ............................................................................... 1 1.2. Sokoban ..................................................................................................... 5 1.3. Outline ....................................................................................................... 6 CHAPTER 2 A SOKOBAN GENERATOR ................................................................... 7 2.1. Wall Templates .......................................................................................... 7 2.2. Goal Placement ......................................................................................... 10 2.3. Box Search ................................................................................................ 11 2.4. Optimizations ............................................................................................ 15 2.5. Run Time .................................................................................................. 17 CHAPTER 3 ONLINE STUDY ..................................................................................... 20 3.1. Database ................................................................................................... 20 3.2. Results ...................................................................................................... 21 CHAPTER 4 LAB STUDY ............................................................................................ 23 4.1. Stroop Test ............................................................................................... 23 4.2. Study Design ............................................................................................. 24 4.3. Study Data ................................................................................................ 26 4.4. Data Transformations ............................................................................... 28 iv CHAPTER 5 ANALYSIS ............................................................................................... 32 5.1. Independent Variables ............................................................................... 32 5.2. Dependent Variables ................................................................................. 32 5.3. Covariables ............................................................................................... 34 5.4. Statistical Models ...................................................................................... 38 5.5. Results ...................................................................................................... 39 5.6. Conclusion ................................................................................................. 42 CHAPTER 6 FUTURE WORK ..................................................................................... 43 6.1. Algorithmic Details ................................................................................... 43 6.2. Other Games ............................................................................................. 43 6.3. Statistics ................................................................................................... 44 APPENDIX A PSEUDOCODE ..................................................................................... 45 APPENDIX B PARTICIPANT SURVEY ..................................................................... 50 APPENDIX C SURVEY RESULTS .............................................................................. 55 APPENDIX D IRB ........................................................................................................ 61 REFERENCES ............................................................................................................... 66 v LIST OF TABLES Page 2.1. The average run time to generate levels of varying sizes with two boxes ............ 17 2.2. The average run time to generate levels of varying sizes with three boxes .......... 18 2.3. The average run time to generate 2 x 2 levels with a varying number of boxes ... 18 3.1. The number of users that played a given number of sessions .............................. 21 3.2. Statistics collected from the Sokoban game released on Kongregate .................... 22 4.1. Pitch and duration of the voice files used in the study ........................................ 24 5.1. Component matrix for the difficulty covariables .................................................. 36 5.2. Component matrix for the Attention Network Test covariables .......................... 36 5.3. Component matrix for the Sokoban practice covariables ..................................... 37 5.4. Component matrix for the Stroop practice covariables ........................................ 37 5.5. Component matrix for the gaming habits covariables .......................................... 38 5.6. Component matrix for the subjective experience covariables ............................... 38 5.7. Log reaction time for the generated levels vs. the hand made levels .................... 39 5.8. Log-odds of accuracy for the generated levels vs. the hand made levels .............. 40 5.9. Log-odds for a missed prompt for the generated levels vs. the hand made levels 41 C.1. Participants' ages................................................................................................. 56 C.2. Participants' gender ............................................................................................. 56 C.3. Participants' ethnicity ......................................................................................... 56 C.4. Participants' marital status ................................................................................. 56 C.5. Highest level of education attained by participants ............................................. 57 C.6. Participants' occupation ...................................................................................... 57 vi C.7. Whether participants had a computer at their job .............................................. 57 C.8. Whether participants had a computer at home ................................................... 57 C.9. Hours per week participants spent on the computer ............................................ 58 C.10. Participants' competency in computer use ........................................................... 58 C.11. Hours per week participants spent on various tasks on a computer..................... 58 C.12. Participants' impressions of various computer related activities .......................... 59 C.13. Game genres enjoyed by participants .................................................................. 59 C.14. Participants' dominant hand ............................................................................... 59 C.15. Participants needing corrective eyewear .............................................................. 59 C.16. Participants diagnosed with some attention disorder ........................................... 60 C.17. Participants impression of the game ...................................................................